AbstractThe purpose of this study was to investigate the mechanical and thermal properties of high-density polyethylene (HDPE) composites reinforced by bamboo pulp fibers (BPF). Using a twin-screw extruder, polymer composites were fabricated using BPF and bamboo flour (BF) as the reinforcement and HDPE as the matrix. Tensile and flexural tests of the HDPE composites were performed to determine the mechanical properties under different conditions. The thermal properties of HDPE composites were characterized by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The results showed that BPF improved the mechanical and thermal properties of the polymer composites more than did BF. The tensile and flexural strength of composites with 30 wt% BPF were increased by 61.46% and 22.94%, respectively, while the tensile and flexural modulus were increased by 84.52% and 27.30%, respectively. Compared to composites with 50 wt% BF, the T5% of composites with 50 wt% BPF increased by 20.18 °C. As the BPF content increased, the storage modulus (E’) and loss modulus (E”) initially increased, followed by a decrease. Compared to the BF/HDPE composites, BPF/HDPE composites reinforced at 30 wt% had a higher storage modulus (E’) and loss modulus (E”) and lower damping parameter (tanδ).